kottke.org posts about The Sixth Extinction

In her book The Sixth Extinction, Elizabeth Kolbert warns that we are in the midst of the Earth’s sixth mass extinction of life, this time caused by humans.

Over the last half a billion years, there have been five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us.

This is a mainstream view of humanity’s effect on the Earth flora and fauna…for evidence, you don’t need to look any further than all of the large mammal species that have gone extinct or are endangered because of human activity.

A more controversial take is offered by Chris Thomas in his recent book, Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction. Thomas allows that there’s a “mini mass extinction” happening, but he also argues that the extreme evolutionary pressure brought by our increasing dominance of our planet’s ecosystems will result in a “sixth mass genesis”, a dramatic increase in the Earth’s biodiversity.

Human cities and mass agriculture have created new places for enterprising animals and plants to live, and our activities have stimulated evolutionary change in virtually every population of living species. Most remarkably, Thomas shows, humans may well have raised the rate at which new species are formed to the highest level in the history of our planet.

Drawing on the success stories of diverse species, from the ochre-colored comma butterfly to the New Zealand pukeko, Thomas overturns the accepted story of declining biodiversity on Earth. In so doing, he questions why we resist new forms of life, and why we see ourselves as unnatural. Ultimately, he suggests that if life on Earth can recover from the asteroid that killed off the dinosaurs, it can survive the onslaughts of the technological age.

The history of life on Earth is a history of extinctions and ecological failures, but it is also a story of formation of new forms and spread of those new forms around the world. The net result has been a gain in diversity. In the human era we are seeing great losses, but we are also seeing all these biological gains of new animals and plants spreading around the world, new hybrids coming into existence. I am not saying there is yet a balance between the two. I accept the losses, but it is also scientifically, and in terms of our human attitudes to nature, extremely interesting to contemplate the gains simultaneously.

If the processes that are going on at the moment continue for a very long time, it is my expectation that the number of species on Earth will grow enormously. We are moving species of existing animals and plants back and forth across the world, so that they are all arriving in new geographic regions. We know when species have done this in the ancient past, they have turned into new species in those different regions. If you fast-forward a million years or a few million years, all of these introduced species that leave surviving descendants will have turned into new species. And that is going to generate many more species. We have effectively created a massive species generator.

That certainly does put an interesting spin on extinction and invasive species.

About 250 million years ago, Earth suffered its fifth (and worst) mass extinction event. Nearly seventy percent of land species disappeared. And they got off easy compared to marine species. Are we headed for another mass extinction on Earth? I’m not ready to break that news. But something unusual is definitely going on and extinction rates seem to be speeding up. Here’s an interesting chat with Elizabeth Kolbert, author of The Sixth Extinction.

The worst mass extinction of all time came about 250 million years ago [the Permian-Triassic extinction event]. There’s a pretty good consensus there that this was caused by a huge volcanic event that went on for a long time and released a lot of carbon-dioxide into the atmosphere. That is pretty ominous considering that we are releasing a lot of CO2 into the atmosphere and people increasingly are drawing parallels between the two events.